The prime mover muscle of the shoulder is the deltoid muscle. The shoulder joint performs extension, abduction and rotation movements. According to the "ACE Personal Trainer Manuel," an isometric exercise is "a high-intensity contraction in the muscle with no change in muscle length." Isometric training only develops strength at the joint angle where the contraction occurs. These isometric shoulder exercises are used for strength or rehabilitative purposes. When performing these exercises, it is important to keep breathing as holding your breath can drastically elevate blood pressure. As a result, people with hypertension should avoid doing isometric exercises.
Isometric Lateral Extension
To build strength in the deltoid muscle, you can perform a lateral extension with a dumbbell or a resistance band. The muscle fibres contract to increase strength and the isometric force output. For example, if you can complete an isometric hold at 6.8 Kilogram, then your force output is 6.8 Kilogram. The joint movement here is shoulder flexion.
To perform this exercise, grab a dumbbell in each hand with your hands in front of your pelvis. Engage the core muscles and lift your right arm to shoulder height. Hold for 10 seconds and lower your right arm. Repeat the same movement with the left arm. If you feel your chest is extending backward, you can either use a lighter hand weight or place your back against a wall. Repeat two to three more times.
Isometric External Rotation Exercise
This exercise is effective for strengthening the rotator cuff. The rotator cuff consists of four muscles, including the supraspinatus, infraspinatus, subscapularis and the teres minor. External rotation is useful for shoulder rehab and to restrengthen the rotator cuff after injury. The joint movement is shoulder rotation.
To perform this exercise, stand against a wall with your arm at a 90 degree angle at the elbow. Next, press your forearm against the wall for 10 seconds. Slowly release the arm and repeat three to five more times. For strength purposes, hold a light dumbbell in your hand with your arm at 90 degrees. Slowly rotate your arm away from the body with your elbow placed into your side. Hold when you feel the contraction in the shoulder and the shoulder blade.
Isometric Shoulder Abduction
This exercise is designed to target the shoulder abductors and the middle deltoid. Abduction exercises require light dumbbells since abductor muscles are not exceptionally strong. The joint movement here is shoulder abduction.
To perform the exercise, stand with the feet shoulder width apart with a soft bend at the knees. Hold a dumbbell in each hand with the arms next to the side of the body. Engage the core and slowly lift the arms to shoulder level. This exercise replicates the look of a letter "T." Hold for five seconds and slowly lower the arms toward the hips. Repeat three to five more times.